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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

CRUDE PETROLEUM

339

1.  DETECTION,    (a) Hard asphalt.    About 0-3 gram of the oil is shaken
in a test-tube with 20 c.c. of petroleum ether (D not above 07) and left
overnight; any hard asphalt present is deposited in blackish flocks soluble
in benzene.

(b) Soft asphalt. About 0-5 gram of the oil is dissolved in a test-tube
in 15 c.c. of ether and the liquid treated with 7-5 c.c. of 96% alcohol; any
soft asphalt present is precipitated in the form of flocks, which unite to a
viscous mass adherent to the walls of the tube and soluble in benzene.

2.  QUANTITATIVE DETERMINATION,    (a) Hard asphalt.    About 5 grams
(or more, with a product poor in asphalt) of the oil are shaken in a litre flask
with 200 c.c. of the petroleum ether used for the qualitative test and left
at rest for a day.    The liquid is then decanted on to a pleated filter, to
which also the insoluble substances are transferred, flask and filter being
washed with benzine until a few drops of the filtrate leave no oily residue
on evaporation.   The insoluble residue on the filter is at once dissolved in
hot benzene, the solvent evaporated in a tared dish and the residue dried
at 105° and, when cold, weighed.

(b) Soft asphalt. 5 grams of the product are dissolved, in a bottle
fitted with a ground stopper and of about 300 c.c. capacity, in 25 volumes
of ether, 12-5 volumes of 96% alcohol being run in to the solution, drop by
drop and with shaking, from a burette. After standing for 5 hours at 15°,
the liquid is filtered and the bottle and filter washed with the alcohol-ether
mixture (1:2) until the washing liquid lea.ves no oily residue, or at most
traces of pitchy substances, on evaporation.

The precipitate, which may contain solid paraffin as well as asphalt,
is dissolved in benzene, the solution evaporated, the residue treated re-
peatedly in the hot with 96% alcohol (about 30 c.c.) until the alcoholic
extracts no longer deposit solid paraffin on cooling. The residue, consisting
only of the soft asphalt, is dried for 15 minutes at 105° and weighed.

For precipitating the asphalt in mineral oils, besides benzine and alcohol-
ether, also butanone,1 amyl alcohol and ethyl acetate have been proposed.

Different solvents precipitate asphaltic substances in different quantities
and of different qualities, so that the analytical results are only relative and
not absolute.

6. Behaviour towards Concentrated Sulphuric Acid.—Concen-
trated sulphuric acid precipitates from crude petroleum asphaltic and
pitchy substances in larger or smaller quantity. In many cases it is, there-
fore, useful to determine these substances, this being done in the following
manner.

In a graduated cylinder with a ground stopper 20 c.c. of the oil are
dissolved in 80 c.c. of petroleum ether (D 0700, and ascertained by pre-
liminary trial to be unattacked by cone, sulphuric acid), the solution obtained
being shaken for a minute with 10 c.c. of cone, sulphuric acid (66° Baume)
and left until the liquid separates sharply into two layers. From the
volume of the dense, black, lower layer is subtracted the volume of acid
added (10 c.c.), the difference representing the quantity of asphalt and
pitchy substances in 20 c.c. of the oil.

1 Schwarz :   Chem. Zeit., 1911, 35. P.
1 Owing to the slight admixture of potassium chloride, 6 grams are taken instead